1. Field of the Invention
This invention relates to a new composition of matter useful in laundry operations. More specifically, an aqueous composition comprising hypochlorite bleach, a buffer, and a builder has been discovered.
The compositions of the invention are unexpectedly stable so as to provide comparable shelf life and aging performance to conventional liquid bleaches. Further, the compositions of the invention contain a builder which substantially improves soil removal during laundry operations. These desirable results have not heretofore been obtainable from a single liquid hypochlorite bleaching composition.
2. Prior Art
Conventional liquid hypochlorite bleaches used for laundry operations contain sodium hypochlorite which aids in removing stains and soils from textiles by virtue of the strong oxidizing power of the hypochlorite ion released in aqueous solution. The bleaching strength of an aqueous solution containing hypochlorite ion is measured as available chlorine. Hypochlorite ion is unstable over a period of time and changes ultimately to chloride ion and chlorate in aqueous solution with a corresponding loss of available chlorine. Overall, the decomposition of hypochlorite ion to chloride represents an undesirable loss of oxidizing power of the solution during shelf life. A conventional aqueous hypochlorite bleach with 5.25 nominal weight percent sodium hypochlorite should have a calculated amount of 5.0 percent available chlorine. Several months shelf life with at least this nominal amount of hypochlorite is assured by initially preparing a formulation with 5.7 to 5.8 weight percent sodium hypochlorite.
An aqueous solution of sodium hypochlorite is inherently basic as it is the salt of a weak acid (hypochlorous acid) and a strong base (sodium hydroxide). Since it is well known that hypochlorite ion is stabilized by basic solutions, conventional aqueous hypochlorite bleaches usually incorporate small amounts of sodium hydroxide or sodium carbonate, which adjust the solution to a pH of about 10.5 to 12.0. Nevertheless, the decomposition of the hypochlorite proceeds (although at an acceptable rate to provide adequate storage stability).
Another factor which is known concerning aqueous hypochlorite bleaching systems is that generally increasing the ionic strength of these conventional hypochlorite solutions further decreases the stability of the hypochlorite. As a consequence, although sodium carbonate buffering systems do somewhat retard the instability of the hypochlorite species by raising the pH, the use of additional soluble components (which would increase the solution's ionic strength) has appeared to be foreclosed. Thus, although bleaching systems which incorporate desirable builder components are known in the dry (non-aqueous) state, aqueous solutions of these dry bleaching systems would not have an acceptable shelf life.